Gear-generating tool.



E. J. LEES.

GEAR GENERATING TOOL.

APPLICATION rum) JULY 13, 1909.

Patented Feb. 10, 1914.

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TED STATES PATENT OFFICE.

ERNEST J. LEES, 0F CLEVELAND, OHIO, ASSIGNOR TO THE LEES-BRADNER COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

GEAR-GENERATING TOOL.

Specification of Letters Patent.

Application filed July 13, 1909.

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Serial No. 507,450.

To all whom it may concern Be it known that I, ERNEST J. LEES, a citizen of the United States, resident of Cleveland county of Cuyahoga, and State of Ohio, have invented a new and useful llmprovement in Gear-Generating Tools, of which the following is a specification, the principle of the invention bein herein explained and the best mode in w iich I have contemplated applying that principle, so as to distinguish it from other inventions.

My invention relates to gear-generating tools of the type having an axis of rotation, and used in geargenerating machines wherein the teeth are generated by continuous rotatory movement of the tool, and

of the blank upon which the teeth are gen .'erated.

The object of the invention is to generate gear-teeth by the above described process, in a more accurate manner than has heretofore, to my knowledgebeen practised.

The said invention consists of means hereinafter fully described, and particularly set forth in the claims.

The annexed drawin and the following description set forth in detail certain means embodying the invention, the disclosed means, however, constituting but one of various mechanical forms in which the principle of the invention may be used.

In said annexed drawing :.Figure 1 is a longitudinal section of a gear-generating tool or hob, of the form now in general use, such section being taken upon the plane indicated by line II in Fig. 2. Said figure also includes a front elevation of a portion of the gear-blank, upon which the tool or hob is shown to be operating. Fig. 2 is a bottom plan of such common type of tool or hob, showing the before-mentioned portion of the gear-blank in connection therewith, in dotted lines. Fig. 3 is a section of a gear-generating tool or hob embodying my invention, showing also a portion of a gear-blank upon which it is illustrated as operating, said section of the hob being taken upon the plane indicated by line TIL-III, in Fig. 4. Fig. 4: is a bottom plan of my improved tool or hob, showing the said portion of the gear-blank in connection therewith in dotted lines. Fig. 5 is an end view of a tool or hob embodying my invention. Fig. 6 is a section of the blank cylinder, fromwhich the tool or hob is formed, said section being taken upon a plane angularly related with reference to and intersecting the middle of the aXisof said cylinder. Fig. 7 is a front elevation of said blank cylinder, shown in the position which it occupies in the lathe while being formed, portions of such lathe being shown in dotted lines.

In the present practice of generating gearteeth in the manner above d'escribed,'the generating tool or hob is formed by cutting helical threads upon a true cylindrical blank, gashing such threads longitudinally along helical lines to form teeth, and then grinding off the teeth from the cutting edge inwardly toward the center, as is well known and understood, and as illustrated in Fig. 5. This tool is then placed in a gear-generating machine, so as to assume a position in which its axis is angularly related to the median plane of the gear-blank upon which the teeth are generated, as shown in Figs. 1 and 2. In this position, by reason of the angular position. given the tool or hob, the sur' face presented to the gear blank is an ellipti cal surface, as shown in Fig. 1. Such presentation of an elliptical surface therefore makes it practically impossible to shape the helical surfaces of the cutting teeth so as to assume a true involute cross-section, assuming for the purposes of illustration, that it is desired to out involute teeth upon the blank, and therefore impossible to present cutting edges in the plane of the gear-blank having the contour of a true and theoretically correct rack. As a result of this method of generating gear-teeth, the latter have been formed only approximately correct, and therefore defectively. To overcome this defect, I have provided my improved tool or hob, which is formed in the following manner: A true cylinder A, Fig. 7, is placed in a lathe which is arranged so that the head and tail stocks thereof may be tilted vertically, so as to bring the. axis of the centers Patented Feb.1,;t$ild.

thereof upon a line inclined to a horizontal cutting tool B having cutting edges of the required theoretically correct cross-section (involute as illustrated) is then placed so that its front cutting edge lies in the plane a; y, and is moved'toward the cylinder so as to just come into contact with the circumference of one of the bases of the cylinder. The lathe is then started so as to rotate the blank A, the feed being arranged so as to cause the tool to travel over the surface of the blank at a rate such as to form the heli cal cuts having the required pitch, the line of travel being that indicated by line :0 y. An ordinary cutting tool is then run across the tool blank to reduce the threads to a common depth. The result of this action is to form upon the blank a surface which is geometrically known as the lateral surface of an hyperboloid of one sheet, and the lateral surface of the finished thread will lie in this hyperboloid surface, as shown in Fig. 4. This blank is then taken and gashed longitudinally along parallel lines extending longitudinally and corresponding in angularity with the angularity of the axis with reference to the horizontal plane, to form cutting teeth. These teeth are cut back from the longitudinal cutting edge inwardly toward the center, in the usual manner, as shown in Fig. 5. In this manner, a series of groups of teeth,are formed, having cutting edges lying in straight lines, as shown in Fig. 5, so that when the hob or tool is presented to the gear-blank upon which it is to operate, cutting edges will be presented in planes parallel with the median plane of the gear-blank, having a true rack formation with cutting edges theoretically correct, as indicated in Fig. 3. A longitudinal section, therefore, taken upon the plane indicated by line III-III would have its outer extreme edges lying in the opposite sides of a rectangle, as indicated in dotted lines in Fig. 5.

In forming the tool in the above described manner, it will be noted that the depth of the cut of the tool B will vary from a minimum at the beginning to a maximum at the center, and then decrease similarly toward the end of the out.

In starting the thread-cutting tool upon a cylindrical blank in the manner above described, it will be noted that while cutting the threads, the tool will cut into the blank more deeply in the middle thereof than at either end, so that the strain on the tool will vary from a minimum when working at the extreme ends of the blank, to a maximum at the center. In order to make the work of the tool uniform, an ordinary cutting tool may be run across the blank so as to first form an unthreaded surface having the true form of an hyperboloid of one sheet. The lathe being now arranged to feed for threadcuttmg, and the tool being applied to the blank, it will be seen that the thread may be cut and the tool always caused to cut away an equal amount of material in form-- ing the thread, thereby making the strain on the tool uniform throughout its operation. The tool for forming the threads may then be applied to the blank in the manner before described. A blank so prepared before the thread cutting tool is applied would therefore have a true rectangular section on the plane indicated by the line a; y, and a section taken upon its axis would be bounded upon two opposite sides by curved lines having the form of arcs of hyperbolas.

The term cutting edges as herein used comprehends the top and side edges of the front end of each tooth. The top cutting edges of all teeth are located as stated in the surface of a hyperberloid of one sheet; and likewise corresponding parts of the side cutting edges are located in similar geometrical surfaces. The side cutting edges are the edges which shape or generate the side faces of the teeth which the described tool cuts in forming a gear; and these side edges are therefore the most important cutting edges. Therefore the location of corresponding parts of these side cutting edges 7 in the geometrical surfaces specified is an essential part of the construction.

Having fully described my invention, what I claim therefore and desire to secure by Letters Patent is:

1. As a new article of manufacture, a gear-generating tool having cutting edges located in the surface of an hyperboloid of one sheet.

2. As a new article of manufacture, a geargenerating tool of circular cross section having cutting edges, arranged in straight lines without the axis of the tool and angularly related to such axis.

3. As a new article of manufacture, a gear-generating tool of circular cross section, and having a longitudinal section upon a plane intersecting the tools axis at an angle, each of the two opposite longitudinal edge portions of such section having the contour of a true rack.

4. As a new article of manufacture, a gear-generating tool provided with a plurality of cutting teeth arranged helically about the axis of the tool, the cutting edges of such teeth being located in the lateral surface of anhyperboloid of one sheet.

5. As a new article of manufacture, a gear-generating tool having an axis of rotation, and provided with a plurality of cutting teeth; groups of such teeth having cutting edges arranged in straight lines angularly related to such axis.

6. As a' new article of manufacture, a gear-generating tool having an axis of rotation, and provided'with a plurality of cutting teeth; groups of such teeth having cut- Ill 30 1,086,542 &

ting edges arranged in straight lines angugear-generating tool-blank having an hy- 1w larly relateol to such axis and lying in the perboloid of one sheet as its lateral surface. lateral surface of an hyperboloid of one Signed by me this 12th day of July, shget.A f 1909. 5 s a new article of manu acture, a

gear-generating tool-blank having a rectan- ERNEST LEES' gular section in a plane angularly located Atbested bywith reference to its axis. WM. E. MILLER,

8. As a new article of manufacture, a WINIFRED WALTZ. 

